Classes View

RDFS and OWL classes are essentially sets of instances. These sets have formal descriptions that specify the requirements for membership in the class. Note that instances may belong to more than one class.

Supported Classes

Using TopBraid Composer you can create:

• RDFS classes - these are typically created as subclasses of rdfs:Resource. You should use rdf:Properties only if you are building an RDFS ontology. For more information on how to configure Composer to be an RDFS editor, see Classes View Preferences and Properties View Preferences.
• OWL classes - these are typically created as subclasses owl:Thing.
• Instances of other metaclasses - user-defined metaclasses are arbitrary subclasses of rdfs:Class, and you can create instances of these metaclasses just like normal classes. Many OWL (DL) users don't use metaclasses, but metaclasses might be useful to specify which properties are relevant for certain kinds of classes.

Classes Hierarchies

Classes are organized in hierarchies, using the rdfs:subClassOf property. Note that a class may be a subclass of more than one parent class. The parent - subclass relationship may be specified explicitly (asserted) or inferred. For example:

• You may declare a class of Man to be a subclass of a class Person and
• You may declare a class of Driver to be an intersection of a class Person with an anonymous class of all Things that have driver licenses. When you invoke the Run Inferences function with an OWL DL inference engine selected, it will be inferred that Driver is a subclass of Person. The class hierarchy in the Classes View will change to reflect the inference.

In OWL, classes are often defined using local properties restrictions and other axioms such as disjoint, intersection and union.

In RDFS (and sometimes in OWL) classes are declared to be in a domain or a range of a property. Note that, unlike in object oriented modeling, subclasses do not inherit properties that have their parent classes in the domain. They do 'inherit' the properties specified as local restrictions for their parent class. You can see these restrictions in the Inheritance View. Be aware though that the notion of inheritance does not have exactly the same meaning in OWL as it does in the object oriented models. If you are aiming at object-oriented semantics, you may want to use SPIN, and in particular only use rdfs:Classes that have spl:Attributes as their spin:constraints.

Using the Classes View 

The Classes View shows all the classes present in the ontology or its imports. This includes classes defined in the ontology as well as built-in classes of RDFS and OWL that were configured to be visible. See Classes View Preferences on how to configure what is visible in the Classes View.

In the default configuration, the Classes View will start with rdfs:Resource, but you can configure it to start with owl:Thing in the context menu of the view. This setting will be remembered for each file, but the root will be reset to rdfs:Resource if the ontology defined RDFS classes or has instances of a special classes such as owl:AllDifferent. In the following screenshot, the Classes View has been configured to start with owl:Thing, and to display the number of instances behind the class names:

There is also an option to Hide system classes, which means that classes from certain system namespaces will be hidden from view. These namespaces include RDFS, OWL and SPIN.

In addition to the subclass hierarchy described above, the Classes View can also be switched to a mode in which classes will be Grouped by namespace. This mode makes it easier to see locally defined classes, but does not represent the class hierarchy at all, and thus also makes editing subclass relationships less intuitive.

Using the Classes View, you can create new classes, define subclasses, modify and delete classes. You can also move classes between ontologies.